1. Field of the Invention
The present invention relates to a camera focal plane shutter in which a shutter blade for opening and closing an exposure aperture is directly driven by an electromagnetic drive source.
2. Description of the Related Art
As conventional camera focal plane shutters which are mounted in cameras and driven by electromagnetic actuators, for example, those disclosed in Japanese Unexamined Patent Publications No.56-99330 and No.62-223736, and Japanese Unexamined Utility Model Publication No.63-26831 have been generally known.
The camera focal plane shutter disclosed in Japanese Unexamined Patent Publication No.56-99330 is provided with, as shown in FIG. 1, a set screw 2 which can be contacted by a drive pin 1a connected to drive arm 1 so as to position the shutter blade at a predetermined starting position (operation starting position). The set screw 2 is screwed and fitted to a curved piece 3a of a base plate 3, and by adjusting the screwing position, the contact position of the drive pin 1a with the set screw 2, that is, the starting position of the shutter blade is adjusted.
The camera focal plane shutter disclosed in Japanese Unexamined Patent Publication No.62-223736 is provided with a position restricting member which can restrict the starting position of the shutter blade and adjust the position of the shutter blade. Furthermore, the camera focal plane shutter disclosed in Japanese Unexamined Utility Model Publication No.63-26831 uses the edge of a slot made in the base plate to restrict the starting position of the shutter blade.
However, in the camera focal plane shutter disclosed in Japanese Unexamined Patent Publication No.56-99330, when the electromagnetic actuator is driven rearward to return the shutter blade to the starting position after an exposure operation is finished, the drive pin 1a directly collides with the set screw 2, and this causes a collision noise, and when the shutter is repeatedly operated, the shutter may be broken. Therefore, the shutter has a problem in durability.
On the other hand, to return the shutter blade to the starting position, it can also be considered that the operation speed is lowered by lowering the driving force of the electromagnetic actuator, however, in this case, problems occur in that the operation sequence lengthens and the frame speed lowers when carrying out serial photographing.
Furthermore, in the camera focal plane shutters disclosed in Japanese Unexamined Patent Publication No.62-223736 and Japanese Unexamined Utility Model Publication No.63-26831, power supply (energization) in a direction opposite to the operation direction is always required immediately before operating, and a problem may occur due to an impulse force when positioning as mentioned above.
The present invention has been made in view of the above-mentioned circumstances, and the object thereof is to provide a camera focal plane shutter which has excellent durability while having a simple structure and enables easy positioning of the shutter blade at an operation starting position and adjustments of the operation starting position.
A camera focal plane shutter according to a first aspect of the present invention comprises a shutter blade which opens and closes an exposure aperture to carry out exposure; an electromagnetic drive source for directly driving the shutter blade; an interlocking member for interlocking with the shutter blade; and a positioning means for positioning the shutter blade at an operation starting position. This positioning means has a contact member which can come into contact with the interlocking member and is movably supported; a pushing member for producing (applying) a pushing force to push the contact member against the interlocking member; and a stopper for stopping the contact member at a predetermined position against the pushing force of the pushing member.
According to this construction, when the shutter blade is positioned at the operation start position, the interlocking member comes into contact with the contact member to retreat the contact member by a predetermined amount against the pushing force of the pushing member. During this motion, the impulse force is eased, and the pushing force of the pushing member charged by the retreat of the contact member pushes back the contact member to come into contact with the stopper, whereby the shutter blade is positioned at the operation starting position.
That is, since the positioning means positions the shutter blade while easing the impulse force due to the inertial force of the shutter blade, a collision noise is suppressed, part breakage is prevented, and durability is improved.
The above-mentioned construction may be arranged so as to include an absorbing (shock absorbing) member which comes into contact with the interlocking member to ease an impulse force after the contact member comes into contact with the interlocking member when the shutter blade is returned to the operation starting position after an exposure operation.
According to this construction, the contact member makes first absorbing action, and following this, the absorbing member makes second absorbing action, so that the impulse force can be securely absorbed and eased.
The above-mentioned construction may be arranged so that the interlocking member is a drive arm to which a driving force is directly applied from the electromagnetic drive source and which is connected to a part of the shutter blade, the contact member is a swing arm supported around a predetermined shaft in a swinging manner, and the pushing member is a torsion spring which is disposed around the predetermined shaft, and which is latched on the stopper at one end and is latched on the swing arm at the other end.
According to this construction, to position the shutter blade at the operation starting position, the drive arm comes into contact with the swing arm to rotate and retreat the swing arm by a predetermined amount against the pushing force of the pushing member. During this motion, the impulse force is eased, and by the pushing force of the torsion spring charged by the retreat of the swing arm, the swing arm is rotated in the opposite direction and comes into contact with the stopper, whereby the shutter blade is positioned at the operation starting position.
A camera focal plane shutter according to a second aspect of the present invention comprises a shutter blade which opens and closes an exposure aperture to carry out an exposure operation; an electromagnetic drive source for directly driving the shutter blade; an interlocking member for interlocking with the shutter blade; and an elastic member, one end of which is fixed and the other end of which can elastically deform when coming into contact with the interlocking member so as to position the shutter blade at the operation starting position.
According to this construction, to position the shutter blade at the operation starting position by means of a driving force of the electromagnetic drive source, when the interlocking member collides with the elastic member due to an inertial force, the elastic member elastically deforms and absorbs the impulse force, and thereafter, by means of an elastic energy charged by the deformation, the interlocking member is pushed back to position the shutter blade. Therefore, even in a simple structure, a collision noise is suppressed, part breakage is prevented, and durability is improved. By only adjusting the attaching angle of the elastic member, the operation starting position of the shutter blade can be properly set at a desired position.